Wireless modem

Abstract

A modem transmits data between a computer and a telephone line. The modem features a base unit which receives a data signal from the telephone line and which transmits the data signal over a wireless link. A device receives the data signal over the wireless link and outputs an analog data signal that corresponds to the data signal. A modem card receives the analog data signal from the device, digitizes the analog data signal to produce a digital signal, demodulates the digital signal, and provides an output digital data signal to the computer.

What is claimed is:  
     
       1. Modem circuitry for establishing a communication link between a computer and a device that receives a modulated analog data signal over a wireless link, the modem circuitry comprising: 
       a coder/decoder for generating a digitized signal based on the modulated analog data signal, the coder/decoder including a three-conductor interface to a three-conductor cable over which all signals are exchanged with the device, the three-conductor cable comprising a first conductor to transmit signals to the device that are destined for a network, a second conductor to receive signals from the device, and a third conductor that acts as a shared ground for the first conductor and the second conductor; and  
       a processor for demodulating the digitized signal to produce a digital data output signal.  
     
     
       2. The modem circuitry of  claim 1 , wherein the device comprises a wireless telephone and the three-conductor interface comprises a headset interface on the wireless telephone. 
     
     
       3. The modem circuitry of  claim 1 , wherein modulated analog data signal uses QAM modulation. 
     
     
       4. The modem circuitry of  claim 1 , wherein: 
       the modulated analog data signal has substantially no nonlinear distortion; and  
       the processor performs echo canceling on the digitized signal.  
     
     
       5. The modem circuitry of  claim 1 , wherein the modulated analog data signal is transmitted over RF using digital frequency modulation. 
     
     
       6. The modem circuitry of  claim 1 , wherein the modulated analog data signal is transmitted over RF using analog frequency modulation. 
     
     
       7. A modem for transmitting data between a computer and a telephone line, comprising: 
       a base unit which receives a data signal from the telephone line and which transmits the data signal over a wireless link;  
       a device which receives the data signal over the wireless link and which outputs an analog data signal that corresponds to the data signal; and  
       a modem card which receives the analog data signal from the device, digitizes the analog data signal to produce a digital signal, demodulates the digital signal, and provides an output digital data signal to the computer, the modem card including a three-conductor cable interface for a three-conductor cable over which all signals are transmitted between the device and the modem card, the three-conductor cable comprising a first conductor to transmit signals to the device that are destined for a network, a second conductor to receive signals from the device, and a third conductor that acts as a shared ground for the first conductor and the second conductor.  
     
     
       8. The modem of  claim 7 , wherein 
       the modem card receives a digital data signal from the computer, generates a digitized analog signal, converts the digitized analog signal to an analog data signal, and outputs the analog data signal to the device;  
       the device receives the analog data signal and outputs an RF signal that corresponds to the analog data signal to the base unit over a wireless link; and  
       the base unit receives the RF signal over the wireless link and outputs a data signal that corresponds to the RF signal over the telephone line.  
     
     
       9. The modem of  claim 7 , wherein the modem card receives the analog data signal from the device over the three-conductor cable. 
     
     
       10. The modem of  claim 7 , wherein the device comprises a wireless telephone that is dialed manually to establish a data link between the computer and the telephone line. 
     
     
       11. The modem of  claim 7 , wherein: 
       the base unit comprises circuitry which limits an amount of nonlinear distortion in the data signal; and  
       the modem card comprises circuitry which performs an echo canceling routine on the digital signal.  
     
     
       12. The modem of claims  11 , wherein the circuitry in the base unit comprises an automatic gain controller and the circuitry in the modem card comprises a processor. 
     
     
       13. The modem of  claim 11 , wherein the echo canceling routine performed by the circuitry in the modem card comprises a linear echo canceling routine. 
     
     
       14. The modem of  claim 7 , wherein: 
       the base unit and the device run error detection routines for detecting an error in the data signal; and  
       when an error is detected in the data signal, the base unit and the device switch to a clear frequency channel over which the data signal is transmitted.  
     
     
       15. The modem of  claim 14 , wherein the error detection routines use a parity bit to check for the error in the data signal. 
     
     
       16. The modem of  claim 7 , wherein the device comprises a cordless telephone handset and the base unit comprises a cordless telephone base unit. 
     
     
       17. The modem of  claim 7 , wherein the device comprises a cellular telephone and the base unit comprises a cellular base station. 
     
     
       18. A method of transmitting data from a telephone line to a computer using a modem card connected to a wireless telephone handset, the wireless telephone handset communicating with the telephone line via a base unit, the method comprising: 
       establishing a connection from the computer to the telephone line via the modem card, the telephone handset, and the base unit;  
       receiving a data signal from the telephone line at the base unit;  
       reducing overload and nonlinear distortion in the data signal using an automatic gain control circuit located in the base unit to keep a peak amplitude of the data signal in a predetermined linear amplification region;  
       transmitting the data signal from the base unit to the wireless telephone handset over a wireless link;  
       transmitting an RF modulated voiceband data signal that corresponds to the data signal from the telephone handset to the modem; and  
       receiving the voiceband data signal at the modem, digitizing and demodulating the voiceband data signal, and outputting a digital data signal to the computer.  
     
     
       19. A modem for transmitting data between a computer and a telephone line, comprising: 
       a base unit which receives a data signal from the telephone line and which transmits the data signal over a wireless link, the base unit including an automatic gain control circuit which reduces overload and nonlinear distortion in the data signal by keeping a peak amplitude of the data signal in a predetermined linear amplification region;  
       a device which receives the data signal over the wireless link and which outputs an analog data signal that corresponds to the data signal; and  
       a modem card which receives the analog data signal from the device, digitizes the analog data signal to produce a digital signal, demodulates the digital signal, and provides an output digital data signal to the computer.  
     
     
       20. The modem of  claim 19 , wherein the modem card includes a coder/decoder that digitizes the analog data signal to produce the digital signal. 
     
     
       21. The modem of  claim 20 , wherein the coder/decoder comprises: 
       a three-conductor interface to a three-conductor cable over which all signals are exchanged with the device, the three-conductor cable comprising a first conductor to transmit signals to the device, a second conductor to receive signals from the device, and a third conductor that acts as a shared ground for the first conductor and the second conductor.  
     
     
       22. The modem of  claim 19 , wherein the device comprises a wireless telephone that is dialed manually to establish a data link between the computer and the telephone line. 
     
     
       23. The modem of  claim 19 , wherein the modem card comprises circuitry which performs an echo canceling routine on the digital signal. 
     
     
       24. The modem of  claim 23 , wherein the echo canceling routine performed by the circuitry in the modem card comprises a linear echo canceling routine.